Sydney edward thacker ewing and joseph leonard willey



illy 17, 1923. 1,461,977

' S. E. T. EWING ET AL ORE REDUCTION Filed Aug. 30. 1922 2 Sheets-Sheet l N .YQQ ql WNQQWQ BubmNuvl @WSN July 17, 1923.

1.461.977 S. E. T. EWING ET AL ORE REDUCTION Filed Aug. 30. .1922 2 Sheets-Sheet 2 www Patented July 17, 1923.

UNITE@ SYDNEY EDWARD TEACHER EWINO- AND JOSEPH LEONARD W'ILLEY, OF JOHANNES- BURG, TRANSVAAL, SOUTH AFRICA.

ORE REDUCTION.

Application led August 30, 1922.

To all whom t may concern.'

Be it known that ive, 'Srnnnr Eaux-inn Trrnciinn Eivind and lossen Leontine lVILLnY, British subjects, both residing at Corner House, Commissioner Street, Johannesburg, Transvaal Province, Union of South Africa, have invented certain neiv and useful Improvements in Ore Reduction, of Which the following is a specification.

The present invention has reference to the reduction of ores, and especially gold ores, by processes involving tube-milling.

Tn the usual methods of reducing' gold ores the tube mill performs the function of line grinding 'a product which has alrezulybeen successively reduced firstly by roel; breakers and secondly by stamps or ball mills (in which metal balls are used as the grinding` charge). The stamp or ball mill product varies in size from Q00 mesh up to inch, or in some cases l inch, mesh and its individual fragments are of generally cubical form without sharp angularities.

Tn order to effect the reduction of this stamp or ball mill product in the tube mill, it is necessary to feed into the tube mill, with said product, a proportion of large pebbles which are usually pieces of orc selected from the ore stream before the latter reaches the breakers; They average in size ,from 6 to T inch cubes and are added in the proportion of usually live to seven per cent of the regular mill feed,i. e., the stamp or ball mill product. The tube mill. ellluent is commonly divided into three products namely (l) fine sand and slime which is the finished product, (2) coarse sand which is insufliciently reduced andA (3) `so called reject pebbles. The first tivo products represent the original mill feed in a more comminuted form, together With so much of the grinding charge as has become coinminuted to their grade. The coarse sand is returned bythe classifiers to the tube mill feed, so that the original tube mill feed re mains in the tube mill circuit until it is fully comminu'ted. The third product, namely, the reject pebblesf7 consists of elements of the original grinding charge which on account of their roundness and relatively small size have become inefficient for grinding purposes. If they are of ore material, they are recovered and crushed, e. g., in the Serial No. 585,291.

stamp mill, to the regular tube mill feed size and mingled with-the feed to the tube mill.

The present invention is a method of operating;- ivith a tube mill whereby on the one hand the ratio of reduction Within the `same is increased and on the other hand a higher perizentage of finished pulp in the tube mill circuit eiiluent is obtained Without that decrease in the rate of feeding which would be necessary to effect the same result under present practice. This renders feasible and economical a process of ore reduction Which involves the use of the tube mill and pebble crackers assisted or not by rock breakers, obviates the necessity of the stamp mill, ball mill, disc crusher, rolls or other crushing appliances hitherto deemed necessary to malte a product suitable for tube-milling; and by the economical production of a one product pulp with its concomitant advantage of simplified treatment, makes possible, in many cases, the elimination of the processes of amalgamation and sand treatment.

The invention consists in a method of orc reduction involving` the use of a tube mill in Which the regular tube mill feed material consists of,-or contains-a large proportion of large and angular fragments of ore; and in which constituent pieces of such feed material which have become rounded and therefore inelicient for comminution, are Withdrawn from the tube mill, broken to make an angular product, and returned to the mill.

The large and angular ore fragments which it is proposed thus to feed to the mill are best represented by those present in run of mine gold ore; and the invention contemplates leeding run of mine ore directly to the tube mill in appropriate cases; in which event the Whole of thereduction is effected by the tube mill, supplemented by the reject pebble cracker. As however the size of material Which can be economically fed to a tubo mill depends upon the size and prop'ortions of the mill itself, it is desirable in many cases and is Within the scope of the invention, to break the larger pieces of rock before they are fed to the mill. Tf the larger pieces are thus broken, it is usually desirable to feed to the mill a proportion of selected pebbles, as in the ordinary practice.

It appears that as the result of thus feeding large and angular ore fragments as the regular tube mill feed, instead of stamp or ball mill product, a material modification of the reduction process within the mill brought about. Vhilst doubtless a considerable amount of reduction is done by the progressive division by fracture of individual pieces into smaller and smaller pieces, there is clear evidence that a greater' part than hitherto is taken by the attrition of the angular prominences Iof the larger pieces. This appears to effect comminution at a rapid rate until the angularities disappear, when the resulting rounded pebbles become an inert constituent of the charge and if allowed to accumulate would seriously reduce the capacity of the mill. llhe systematic withdrawal of these rounded pebbles so that they may be broken and again made angular is therefore an important feature of this invention. ln this respect there is an essential diiierence from the withdrawal of reject pebbles in the present practice, where they are the residue of the added grinding charge, the mill feed material being` left in the tube mill circuit until it is reduced, at least to sand. The present method marlrs a distinct departure by withdrawing` tube mill feed in pieces of such size as still to be capable of being broken in a roel: breaker; and this is the only product which, in carrying out the invention, necessarily requires to be thus broken.

The functions of the added pebbles in the present case are `probably different from the grinding function which they exercise in a mill fed with stamp mill or ball mill product; and is rather that of securing effective relative rotation of the elements of the charge.

In the accompanying drawings Figs. I and ll are respectively an elevation and plan showing diagrammatically a plant for carrying out the invention.

Fig. III is a vertical section of the discharge end of the tube mill,

Fig. IV is a face View of the discharge screen therefor and Fig. V is a sectional view of the tube mill inlet trunnion and feed hopper.

The plant shown is one employing a usual. standard size of tube mill, namely, 22 feet long by 5 feet 6 inches diameter, which renders desirable the preliminary breaking of the larger pieces of ore. Accordingly ore is delivered from the shaft bins l to the grizzly 2. ,The grizzly undersize is taken direct to the tube mill ore bin 3 which feeds the tube mill l. The grizzly oversize goes to a single stage breaker' and the broken product is taken, with the grizzly undersize, to the ore bin 3. The selected pebbles are in the usual manner withdrawn from the breaker feed and sent to the pebble bin G for supply to the tube mill; the quantity being as a rule 8 to lO per cent of the total fresh material. passed`into the tube mill.

The material thus delivered to the tube mill bin 3, namely, the grizzly undersize and the single stage breaker product, is, as re-v gards the form of its constituent pieces, adapted for self-comn'iimition in the mill, in that besides being distinctively angular it also contains a considerable proportion of slabby fragments.

As regards the size of this material, we hare found that aproduct passing through grizzlies set at three quarters of an inch apart, together with a corresponding breaker product, is about the least that is eiiciently seifecomminuting in the tube mill. The degrec by which this lower limit may be exceeded dependa upon the proportion of the reiflucti'on which can' economically be allocated to the breaker and the tube mill. respectively and would be determined largely by the dimensions olf the tube mill which it is proposed to use in any particular case. le have found that when using a tube mill of the vfi'iniensions stateiil above economical ref sults with ore from the deep level mines of the Far East lilitwatersrand area have been attained when the material varies from inch to ii inch grizzly product.

rif he usual arrangements for feeding stamp mill or hail mill pulp into the tube mill are not suitable for passing in the large dry fragments contemplated by this invention. lVe have ilonnd however that the difficulty can be overcome by using a hopper 7 open ing into the inlet trunnion 8 of the tube mill il and having a steeply sloping baclr 9; and making the trunnion S of greater internal diameter than is usual. Said hopper 'T receives the ore from the bin 3, the selected pebbles from the bin G, and the sand from th classiiier l0. lf grinding in cyanide is adopted the strong cyanide solution may also be added at this point.

The tube mill discharge arrangements are such as to withdraw from the outlet end of the mill a very much higher proportion than hitherto of large material; in fact we have found it d esirable to withdraw the whole product from the discharge end of the vmill as rapidly as is consistent with maintaining the proper level of the load. in the mill. To accomplish this there is provided an outlet screen ll which is extensivelyv perforated with large aperatures ,19' pret erably slots about l-linches wide and G inches long. There are also provided scoops 13 which at once discharge into the outlet trunnion 14 all material which passes through the screen.

The usual devices are employed for separating the tube mill effluent into the desired constituents. Sand and slime passing through the revolving screen l5 into the launder 16 are conducted thereby to the classifier 10 which separates the coarse sand from the finished product and passes the sand to the hopper 7.

The single linal product from the classilier 10 is shown as being conducted directly to the slime plant 17.

The reject pebbles pass along the screen 15 and are carried by the belt 18 to the pebble cracker 19, the product Yfrom which passes to the ore bin 3.

As mentioned above reject pebbles are re moved in much greater quantity than hitherto; and We have found .it possible and adjvantageous to remore, in this VForm, lrgm ten per cent upwards of the total fresh material fed to the mill as compared with 1- to 2 per cent under present practice. With the particular ores referred to above, we regularly remove 18 to 21 per cent, and the proportion may be increased with appropriate ore and size ot' ieed material.

In the absence of the stamp mill, the pebble cracker 19 constitutes an additional unit oi' the plant rendered necessary by the new process, and to a certain extent it may be regarded as a secondary Crusher, but its Jfunction is more economically peritormed than that of the ordinary secondary Crusher in a stage crushing plant inasmuch as its position in the plant necessitates its operating merely on the residue of material which has ceased to be eiciently self-coniniinuting.

As regards the output of the tube mill, Whilst the average size of the feed is increased many times, the output oit fully comminuted material shows a substantial advance. F or instancetwith the new methods a mill of the standard dimensions stated above, When treating the above mentioned ores, produced per 24 hours 145 to 155 tons of minus 90 mesh product ol which 75% Will pass a 200 mesh screen. It will be evident that if a coarser product is made, the rate of output of the tube mill Will be commensurately increased.

This product is generally suitable tor immediate treatment as a slime product.

We claiml. The improrement in the art ot tubemilling ore which consists in supplying to the tube mill, as the regular mill i'r'eed, ore in large and angular fragments, Withdrawing from the tube mill fragments of said feed material which have become rounded, breaking them, and returning the breaker product to the tube mill.

2. rfhe improvement in the art of tubemilling ore which consists in feeding a run of mine ore to the tube mill as the regular mill feed, withdrawing from the tube mill fragments of said Jfeed material which have become rounded, breaking them, and returning the breaker product to the tube mill.

3. The improvement in the art of tubemilling ore which consists in supplying to the tube mill, as the regular mill feed, ore in large and angular fragments, withdrawing from the tube mill, as reject pebbles, a substantial proportion oit the original mate- .rial lied to the tube mill, breaking the .reject pebbles and returning the breaker product to the tube mill.

4. The improvement in the art of tubemilling ore which consists in supplying a run et' mine ore to the tube mill as the regular mill feed, withdrawing from the 'tube mill, as reject pebbles, a proportion o't' such iced, breaking the reject pebbles, and returning the breaker product to the tube mill.

The improvement in the art oit tubemilling ore which consists in supplying to the tube mill, as the regular mill i'eed, ore in large and angular tragments, `vithdravving` 'lrom the mill, as reject pebbles, not less than teu per cent oi the material originally iied to the tube mill, breaking the reject pebbles and returning the breaker' product to 'the tube mill.

6, The improvement in the art ot' tube milling ore vnicli consists in feeding a run oit mine orc to the tube mill as the regular mill Ytoed. withdrawing from the mill as reject pebbles, not less than ten per cent of the material originally i-'ed to the tube mill, breaking the reject pebbles, and returning` the ln'eaker product to the tube mill.

7. The improvement in the art oil. tubemilling ore which consists in separating the larger pieces from a run of mine ore, breaking them in a single stage, adding the product to the remainder of the run of mine ore, 'fee ling the Whole directly to the tube mill as the regular mill feed, withdrawingfrom the tube mill fragments of said feed material which have become rounded, breaking them, and returning the breaker product to the tube mill.

S. The improvement in the art of tubemilling ore which consists in supplying thereto, as the regular mill ieed, ore in large and angular ragments, withdrawing all material arriving at the discharge end of the tube mill as rapidly as is consistent with maintaining the load in the tube mill, separating pebbles from said material, breaking said pebbles, and returning the breaker product to the tube mill.

In testimony whereof we aliix our signatures.

SYDNEY EDWARD THACKER EWING. JOSEPH LENARD WILLEY. 

